Nine staff members of a Nebraska correctional facility were assaulted by inmates Wednesday, officials said.

Fire and rescue personnel were called to the Lincoln Correctional Facility at around 6:45 p.m. Officials said inmates were refusing to return to their housing units and eventually assaulted nine staff members, according to WOW-TV.

At least six of the staff members were transported to a hospital and three others were treated at the facility. The severity of their injuries is unclear, WOWT-TV reported. All are expected to be treated and released.

The Lincoln Correctional Facility is a medium/maximum custody facility and was on lockdown by nightfall, officials said